[Elecraft] K3 PA temperature reading jumps / hot smell

[Dave Hachadorian]

The 20 meter temperature increase sounds normal to me.  The 10 
MHz and 21 MHz behavior is a little strange.  Here is a link to a 
PA temp experiment that I conducted on both of my K3's:
http://marc.info/?l=elecraft&m=128534687205664&w=2

Dave Hachadorian, K6LL
Yuma, AZ


-----Original Message----- 
From: Felix Hormuth
Sent: Tuesday, June 30, 2015 5:16 AM
To: elecraft at mailman.qth.net
Subject: [Elecraft] K3 PA temperature reading jumps / hot smell

Dear all,

my K3 (S/N 8862) is developing a strange behaviour that is 
beginning
to worry me a bit... Current firmware, assembled as kit, power
calibration just repeated to be sure.

First -- and this is not really new -- from time to time it 
produces
a smell that is best described as 'hot', like in hot resistor, 
hot
transistor and similar. I've never managed to track down the 
source,
though it seems to be related to output power. Sometimes it 
appeared
after just 1 minute of operation (the maximum I do is 100W RTTY 
with
short QSOs and never more than 50% duty cycle) and was then gone
for the rest of the day, sometimes it started a bit later, and 
sometimes
it never appeared. The PA temperature was always fine in these 
cases,
below 50 degC max. Now this smell seems to be increasing and I'm
worried some real damage might develop.
The second new issue is that during TX the PA temperature reading
increases quite fast and then when switching back to RX 
*immediately*
drops back by several deg C.
Example:

- start at PA temp = 33C
- transmit 90W RTTY for 30s on 14MHz into dummy load
--> temperature increases to 43 deg C
- back to RX: temperature drops down instantly to 35 deg C

Now the funny thing is: if I do that on 10MHz, it behaves
completely normal. Temperature increase is just 2C, no drop at 
the end.
That's how it was on 20m in the past as well.
On 15m somewhere in between (+4, and then drop by 2), then on 12m 
and
higher again back to normal.

Anyone with similar observations? Any ideas what to check or test 
or do?

Man thanks for any help,
vy 73, Felix DL2FHO





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